1 1/2yr old male puppy humping my 8 month old female

I have a Shih Tzu, which he's 1yr1/2.I also have a 8month old female kitty. My Shih Tzu is humping the kitty, and my kitty is letting him. She actually sticks her rear out so he can......
Is this normal, and could something happen to either one?

Status

Cast your vote for which answer you think is best!

Answers

Are either of them fixed? Chase (a spayed female) would periodically try and hump our cat when she was going into heat before we had her spayed as well. The cat would often present herself to Chase and make a little trilling noise and dance around.
Perhaps your cat is about to go into heat?